Mount for acoustic transducers



Feb. 24, 1970' i w. J. MUELLER MOUNT FOR ACOUSTIC TRANSDUCERS Filed Jan.20, 1967 2 Sheets-Sheet 1 INVENTOR William J. Mueller 30. l BY TORNEY 4%AGENT Feb. 24, 1970 Q I w. J. MUELLER 29 MOUNT FOR ACOUSTIC TRANSDUCERSFiled Jan. 20, 19s? 2 Sheets-Sheet 2 FIG 3 DISPLACEMENT 0 0 l0 0 2o 3040 5o FORCE 0 I6 20 3o DIIEPTH I DISPLACEME F] G. 5

0 lb 2'0 5 0 D EPTH DISPLACEMENT FF G 6 I o l -l 0 I0 20' 3o DEPTHUnited States Patent O 3,497,729 MOUNT FOR ACOUSTIC TRANSDUCERS WilliamJ. Mueller, Portsmouth, R.I., asslgnor to the United States of Americaas represented by the Secretary of the Navy Filed Jan. 20, 1967, Ser.No. 615,037 Int. Cl. H04]: 13/02 US. Cl. 3109.1 4 Claims ABSTRACT OF THEDISCLOSURE A mounting structure for underwater acoustic transducersutilizes a clamping device for preloading a compliant pressure releasematerial for suspension of the transducer from fixed structure and thetransducer housing. A sandwich arrangement of the pressure releasematerial and portion of the transducer housing provides a push pull typepreloading of the release material relative to the fixed structure fromwhich the transducer is suspended or mounted.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION This invention relates to an underwatertransducing device and more particularly to a hydrophone assembly forutilization under deep depth operational conditions.

FIELD OF THE INVENTION More specifically the invention is directed to animproved resilient mounting structure and a new and novel methoddirected to the manner of preloading the resilient elements of atransducer suspension assembly to provide improved linearitycharacteristics in the overall response of the transducer.

DESCRIPTION OF THE PRIOR ART In prior art transducer mounting structuresvarious types of spring suspensions, diaphragm or bellows supports,rubber mounts and various combinations thereof have been utilized for avariety of purposes. The suspension designs vary with environmentalconditions, the desired operational bandwidth characteristics, thesensitivity and/ or response pattern of interest, the type of transducerand other factors known to practitioners in the art.

Spring type suspension systems have been utilized for a variety ofpurposes including a tuning of the resonance of the overall transducerresponse to a resonant condition at the frequency of intended operation.A suspension and bafile arrangement of this type is shown in US. Patent3,225,326 which issued to Frank Massa on Dec. 31, 1965. A transducermounting assembly incorporating an axial loading system for a pair ofceramic crystals together with a Sylphon bellows for signal baffling anda sponge rubber doughnut type overload prevention device is illustratedin US. Patent 3,048,815 which issued to Edward G. Thurston and Donald W.Knester on Aug. 7, 1962.

The aforementioned patents are exemplary of techniques utilized forunderwater hydrophone applications.

SUMMARY OF INVENTION The instant invention relates to a resilientmounting system for a deep submergence depth hydrophone whichadvantageously may be utilized at various depths. It incoporatesinstrumentalities and techniques for preloading the resilient members ofthe suspension system in a man- 3,497,729 Patented Feb. 24, 1970 ice nerto appreciably enhance the linearity characteristic thereof, therebymaterially reducing undesirable performance variations of a naturenormally resulting from operation of a hydrophone type transducer atvarious depths of submergence in a fluid medium such as sea water.

Transducer elements of the character with which this invention isconcerned require a mounting assembly which will maintain an optimumdegree of rigidly in holding the transducer in place while at the sametime permitting the transducer to vibrate in response to electricalenergy appled thereto in the transmitting mode of operation or in thealternative to acoustic signals to which the transducer is subjected inthe receiving mode of operation. Attempts to achieve the desired degreeof rigidity have been directed to the utilization of layers of compliantmaterials, herein after referred to as pressure release materials.Materials of this character display nonlinear spring constantcharacteristics or modulus of elasticity. Under operational conditionsoccurring at deep submergence depths in a fluid medium the transducer issubjected to high hydrostatic pressure and the mounting system iscompressed and becomes stiffer. This compression and resultant increasedstiifness produces variations in resonant frequency which adverselyafiect the performance of the equipment with which the transducer isutilized.

The instant transducer mounting device incorporates instrumentalitiesfor preloading the pressure release material in a manner providingimproved operation in a more linear region.

.It is a feature of the instant invention to provide an improvedhydrophone mounting system wherein all of the advantages of prior typepressure release material and spring suspension systems are obtainedwhile obviating many of the disadvantages of nonlinearity in response ofthe hydrophone due to suspension system influences.

One object of this invention relates to the utilization ofinstrumentalities for preloading a pressure release material as utilizedin a hydrophone mounting assembly to provide improved linearity of theoperational characteristics of the hydrophone with operation at deepdepths of submergence.

An additional object of the invention relates to the provision ofstructure for providing a push-pull type preloading of the pressurerelease material of a nature wherein as a result of deep depthoperation, one layer of pressure release material is compressed whileanother layer expands.

In correlation with the immediately foregoing object, it is a furtherobject to optimize the linearity of response of the pressure releasematerial in a manner whereby the spring constant of one layer of suchmaterial decreases as the spring constant of the other layer increasesthereby efiecting a cancellation of a large part of the otherwiseexistent variation in response thereof.

Other objects, advantageous and novel features of the invention willbecome apparent from the following detailed description when taken inview of the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic plane view ofa hydrophone mounting apparatus of the instant invention;

FIG. 2 is a diagrammatic elevation view in vertical section taken alonglines 2-2 of FIG. 1, showing typical structure emboding the inventiveconcept of the invention;

FIG. 3 is a graphic illustration showing a plotting of displacement vs.force for pressure release materials as utilized in conjunction with adeep submergence depth hydrophone system;

FIGS. 4, 5 and 6 are graphs of a family of curves showing a plotting ofdisplacement vs. depth for preloaded pressure release materials.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGS. 1 and 2wherein the hydrophone mounting system is indicated generally at 10, thetransducer assembly 11 is shown as comprised of a plurality of activetransducer elements 12, a front mass element 13 and a rear mass element14.

The hydrophone assembly 11 is provided with a radially extending flangemember 15 disposed to project from the periphery of the assembly forpurposes of suspension from a mounting plate 16 by virtue of thepressure release material 17.

The pressure release material preferrably is disposed in a sandwicharrangement with a first layer or ring of pressure release materialdisposed at 18 between the flange member 15 and the mounting plate 16. Asecond ring or layer of pressure reelase material is disposed asindicated at 19, below the flange member 1 6 and the lower most mountingring 20.

In order to provide a desired degree of preloading of the pressurerelease material 17 a suitable clamping device is mounted relative tothe mounting plate 16 and the mounting ring 20. A screw device isindicated at 21 as an example of a suitable clamping device. Other moreelaborate clamping devices may be utilized as desired. Only one clamp isindicated in FIG. 2 of the drawings although it is to be understood thata plurality of such screws are utilized as indicated in FIG. 1, in orderto provide a substantially equal pressure across the layers of pressurerelease material. The pressure release material may be of any materialsuitable for the purpose such for example as a stack of laminations ofonion skin paper.

Adjustment of the screw elements of the clamping assembly provides forvariation in the degree of preloading of the pressure release materialin a manner deemed to be obvious to one skilled in the art and to a.degree permitting operation over any desired portion of the overalloperational range.

In the operation of a hydrophone incorporating a transducer andtransducer mounting system of the aforementioned character, as it isplaced at a desired depth in a body of Water, pressure is applied to thetransducer element or multiple element unit as the case may be. As aresult of the deep operational conditions to which the transducer issubjected, one layer of pressure release material i.e. stack oflaminations for a preferred embodiment, is compressed while the otherstacking layer of pressure release material is permitted to expand.Accordingly, one spring constant characteristic increases for one layer,While that of the other layer decreases, This push-pull arrangementresults in a cancellation of a large part of the otherwise existantvariation in performance of the mounting system and hence an improvementin the overall response of the transducer.

It has been determined that variations may be reduced by factors ofabout 15 to 30.

Referring to FIG. 3 a typical curve for a pressure release material of aconventional nature is indicated at a which illustrates the nonlinearcharacteristics thereof. Transducers are normally operated over a regionas indicated at A. The spring constant or force required for unitdeflection varies from 0.47 units to 1.5 units over this operatingregion. The value of the spring constant may be obtained by taking thereciprocal of the slope of the curve of FIG. 3. The techniques utilizedin the practice of the instant inventive concept envisions operation inthe region of the portion of the curve a as indicated at B. In region Bthe spring constant varies by less than a factor of 3 as compared to anequivalent variation of more than 3 in the region of the curve indicatedat A. The resulting curve for operation in the range at B is indicatedin FIG. 4. The preloading system of the instant invention is consideredfor purposes of illustration as applying a preloading force of 20 unitsto the pressure release material. Hence, the zero point on the depth (orthe force from an external pressure) scale in FIG. 4 occurs at theposition equivalent to the position of 22 units of displacement in FIG.3 due to the initial displacement resulting from the preloading. Theinstant push pull mounting arrangement of FIGS. 1 and 2 providesconsiderably greater reductions in this variation or nonlinearity.

In order to further illustrate the practice of the instant invention,let it be assumed that the clamping screws are adjusted to compress thepressure release laminations of the layers by 14 units of displacement.Referring to FIG. 3 it may be determined that this degree of compressionor displacement of the bottom ring generates an upward force of 10 unitson the flange of the front mass and the upper ring layer generates asimilar downward force. The foregoing relationship is assumed for zerodepth, and accordingly zero force on the upper face of the top mass. Asthe transducer is submerged in a body of fluid such as sea water and toa desired operational depth, the hydrostatic pressure of the Waterproduces a force against the face of the top mass which in turndisplaces the element in a downward direction, i.e. assuming theorientation of the system as being that illustrated in FIG. 2. In theevent the displacement is one unit, the total displacement for the lowerstack of laminations of pressure relief material is 15 units. Referringto FIG. 3 a determination may be made that the upward force generated bythe lower pressure relief material amounts to 11.1 units. Similarly, thedisplacement of the upper ring is 13 units, with a resulting downwardforce of 9.2 units. Accordingly for one unit of displacement theunbalance of force, or the restoring force, is 11.1 minus 9.2 or 1.9units of force.

This point, along with points obtained in a similar manner for othervalues of displacement will provide a plot as indicated in FIG. 3. Thepoints are also plotted in FIG. 5 in which the depth and displacementscales are adjusted in accordance with the magnitude of preloading. Anadditional set of points for an initial bias pressure of 20 units isalso illustrated in FIG. 3 and again in FIG. 6 with the correctedscales.

The reduction in spring constant variations for a mounting systemincorporating the instant inventive concept is indicated by the nearlystraight lines formed by the plotted points of FIGS. 4, 5 and 6. Theinventions are approximately 10% and 20% respectively with the 10 and 20unit force biasing as compared to variations of approximately 300% for asingle layer of pressure release material. The reduction in springconstant variation by factors of 15 to 30 times provides a similarreduction in the variation in resonant frequency of the mounting system.By varying the biasing force applied to the pressure release material,an operating region may be determined for purposes of minimization ofvariations. In the event a particular pressure release material providesa force vs. displacement curve having a knee portion, it has been founddesirable to adjust the biasing to place the bias force in arelationship as indicated at the knee or far enough above the knee toexclude it from the operating region.

Although the preferred embodiment disclosed herein is directed to apush-pull system for reduction in variations of the response ofapparatus embodying a preloading clamping device, it is to be understoodthat the novel method and technique of adjustably preloading thepressure release material is equally applicable to a mounting systemutilizing a single layer or single stack of laminations in lieu of thedual arrangement illustrated and described.

Obviously many modifications and variations of the present invention arepossible in light of the foregoing teachings. It is therefore to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

1. In combination:

a housing;

an acoustic transducer having a pressure responsive surface;

means for mounting said transducer within said housing so as to exposesaid pressure responsive surface to incident acoustic energy,

said means for mounting including;

a supporting member secured to said transducer and extending outwardlytherefrom in a direction parallel to said pressure responsive surface;

a first layer of pressure release material disposed between one side ofsaid supporting member and a portion of said housing;

a second layer of pressure release material disposed on the other sideof said supporting member; and

means for initially establishing a compressive force of a predeterminedmagnitude across both layers of pressure release material,

said last-mentioned means coacting with said layers and said supportingmeans to further compress one of said layers of material Whilesimultaneously relieving the compression on the other of said layerswhenever said supporting means is forced to move in a directionprependicular to said pressure responsive surface by increasing staticpressure on said transducer.

2. The combination as recited in claim 1 wherein said supporting memberis a flange-like annular member surrounding said transducer.

3. The combination as recited in claim 1 wherein said pressure releasematerial is composed of layers of onionskin paper.

4. Apparatus for suspending a transducer within a housing so as toensure movement of said transducer along its longitudinal axis as saidtransducer and housing are submerged to various depths within a fluid medium comprising:

means for mounting said transducer in said housing,

said mounting means including;

a supporting member secured to said transducer and extending outwardlytherefrom in a direction perpendicular to said axis;

at least one layer of pressure release material disposed between saidmember and a portion of said housing for allowing relative movementtherebetween whenever said transducer is subjected to high staticpressures; and

biasing means for initially compressing said pressure release materialby a predetermined amount.

References Cited UNITED STATES PATENTS 2,405,226 8/1946 Mason 340102,430,013 11/1947 Hansell 3108.2 2,448,365 8/ 1948 Gillespie 340102,498,737 2/1950 Holden 34010 2,711,646 6/1955 Mendousse 340-102,891,177 6/1959 Hafner 310-8.2 2,914,686 11/1959 Clements 340103,198,489 8/1965 Finch 310-87 3,222,462 12/1965 Karmann 310-9.13,360,664 12/1967 Straube 340-10 3,370,187 2/1968 Straube 310--9.1

I D MILLER, Primary Examiner US. Cl. X.R. 3108.6; 34010

